HISTORY OF THE LARVAL AND PUPAL STAGES. 85 
For the separation of these different stages of growth useful char- 
acters are found in the size and structure of the legs, and especially 
of the anterior pair, the antenna 1 , and in the development of the wing 
sheaths. It is the rule with insects that with each molt there is a 
decided increase in the size of the head and hard parts generally, and 
with the periodical Cicada especially it is also very doubtful if it ever 
molts without a decided change of the sort indicated. Its life beneath 
the ground in its moist cell over a rootlet is a very quiet one and free 
from any of the wearing action of rain or the drying of the outer air, so 
that the need of a moltiug or change of skin would apparently be much 
less than that in an exposed or much more active insect. It probably 
also very rarely has occasion to burrow to any considerable extent and 
probably often remains for years in the same cell, which it enlarges from 
time to time without change of location. For these reasons the writer 
is inclined to believe that moltings only occur when change of form 
becomes necessary by the increased size of the insect, and this seems to 
be borne out by definite structural peculiarities, which easily permit us 
to recognize the different stages or determine the age of any larva within 
a year or two. The larva of a particular molt or stage of growth will vary 
considerably in size of the body and the softer parts, representing per- 
haps a difference in age in some cases of one or two years, but the hard 
parts will present a very uniform size and character. 
The peculiar structure of the enlarged anterior legs furnishes perhaps 
the best means of distinguishing the adolescent stages of this species 
from other Cicadas and the modification which these limbs undergo 
with the different molts the best means of determining the age of the 
larva 1 . The peculiarities of the anterior legs consist in the enormous 
enlargement of the femora and tibia 1 and their development into struc- 
tures which resemble somewhat the cutting mandibles of biting insects 
or recall the fossorial forelegs of the mole cricket. The peculiar 
structure of these legs is in fact especially designed for digging, tear- 
ing, and transporting earth in the course of the insect's subterranean 
life. As already indicated, the amount of burrowing in the early stages 
is not necessarily very great in any one year, but during the entire 
seventeen years conditions may occasionally arise which will demand 
a considerable activity on the part of the young Cicada. 
The details of the structure of the front legs, which are given in the 
technical description of this species, are quite characteristic and diverge 
notably from the similar parts of other species. The anterior tarsi of 
the periodical Cicada exhibits also a rather peculiar metamorphosis 
during the adolescent life of the species. In other words, during the 
first larval stage and in the pupal stage it is similar to the other tarsi 
but considerably longer, being attached to the inner side of the greatly 
enlarged tibia and at a considerable distance from the claw-like tip of 
the latter. The fore tarsi are of service to the young larva in walking 
and climbing and in the same way to the pupa after its emergence from 
